Because a torque wrench can tighten parts with a predetermined clamping power (tension force), torque wrenches are used conventionally when attaching parts to a vehicle body.
However, as some of the parts are fixed using a large number of bolts, it is hard to distinguish a bolt which is loosely tightened and a bolt which is strongly tightened at a glance, therefore, it is possible that the tightening of some bolts may be overlooked.
To resolve such a problem, Patent Document 1 and Patent Document 2 are suggested.
Patent Document 1 discloses a means to prevent tightening from being forgotten, that is, attach a light emitting device which emits light when clamping has been completed by a torque wrench, this emission of light is detected by a camera, and the position of the bolt on which clamping has been completed by the torque wrench is memorized by a computer.
Patent Document 2 discloses a means to prevent tightening from being forgotten, that is, attach a supersonic wave oscillator to the head of the torque wrench, receive the pulse from the supersonic wave oscillator by 3 receiving antennas, and calculate the position of the bolt on which clamping has been completed using the principle of triangle range-finding, then store the calculated value in a computer.
A LED is used as the light emitting device which emits light when clamping is completed, but if the LED is exposed on the outside, it might be damaged in cases when the torque wrench fell.
Therein, Patent Document 3 suggests the LED be put in a case which has holes, or to provide a light guide leading LED light to the surface of the case.